The pH-, water content-, sample concentration-, temperature- and time-dependences of the UV–vis spectra of the potentially tautomeric azocoupling product
1 in (aqueous) ethanol solutions have been systematically investigated. On the basis of pH-dependence were determined the p
Ka′ values corresponding to three interconnected acid–base equilibria
2b1a3b4b that originate from
1. The four species
1a,
2b,
3b,
4b involved in these equilibria are characterized on the basis of their different visible absorption bands. The hydrazone structure
1a of the initial species is supported by the
1H and
13C NMR data. The dependence of the UV–vis spectra of (aqueous) ethanol solution of
1 upon the water content, dye concentration, temperature or time seems to be due firstly to the acid–base equilibrium
bf3dfc715e2ee38bce80096d45d5df"" title=""Click to view the MathML source"">1a3b. However, some irregularities in these dependences might be interpreted as being caused by eventual superimposition upon the acid–base equilibrium
1a3b of the azo–hydrazone (e.g.
1a1b) and/or aggregation equilibrium. By the time dependence has been observed practically a kind of oscillation of the position of the present equilibrium that is very difficult to explain.
